A processing method implemented by a system (S1; S2) comprising a mobile device, a first server (H-TSP) of a home token service provider, a second server (R-TSP) of a roaming token service provider, a third server (H-SV) of a home banking network (H-NT) and a fourth server (R-SV) of a roaming banking network (R-NT) having specifications that differ from the home banking network, said method comprising successively: - receiving, by the fourth server (R-SV) of the roaming banking network (R-NT), from a first bank system of an acquirer, a roaming token (R-PAN) as part of transaction data characterising a payment transaction performed by a digital wallet application using a mobile payment card in the roaming banking network (R-NT), said roaming token being adapted to allow authentication in the roaming banking network (R-NT) of payment transactions performed by the digital wallet application, wherein the digital wallet application is implemented by the mobile device and the mobile device implements a payment application cooperating with the digital wallet application to perform a payment transaction with respect to the mobile payment card in the home banking network (H-NT), and the mobile device also implements a roaming payment application other than the payment application, the roaming payment application cooperating with the digital wallet application to allow adequate processing of a payment transaction with respect to the mobile payment card while roaming in the roaming payment network (R-NT); - receiving, by the second server (R-TSP) from the fourth server (R-SV), said roaming token (R-PAN) allocated to the mobile payment card for operating in the roaming banking network (R-NT); - obtaining, by the second server (R-TSP), based on the roaming token (R-PAN) and information previously stored in association with said roaming token (R-PAN), a home token (H-PAN) allocated to the mobile payment card for operating in the home banking network (H-NT) other than said roaming banking network (R-NT), said home token (H-PAN) being adapted to allow authentication in the home banking network (H-NT) of payment transactions performed by the digital wallet application; - receiving, by the first server (H-TSP), the home token (H-PAN) obtained by said second server (R-TSP); - obtaining, by the first server (H-TSP), based on the home token (H-PAN) and information previously stored in association with said home token (H-PAN), a primary card number (C-PAN) of the mobile payment card for operating in the home banking network (H-NT); and - sending, by the third server (H-SV), to a second bank system of an issuer of the mobile payment card, a transaction request comprising the primary card number (C-PAN) obtained by the first server (H-TSP) for allowing the payment transaction in the home banking network (H-NT) using said mobile payment card, wherein the obtaining by the second server (R-TSP) and the obtaining performed by the first server (H-TSP) perform a double detokenization to achieve interoperability between the roaming banking network (R-NT) and the home banking network (H-NT), while ensuring that the payment transactions are performed securely. - receiving, by the fourth server (R-SV) of the roaming banking network (R-NT), from a first bank system of an acquirer, a roaming token (R-PAN) as part of transaction data characterising a payment transaction performed by a digital wallet application using a mobile payment card in the roaming banking network (R-NT), said roaming token being adapted to allow authentication in the roaming banking network (R-NT) of payment transactions performed by the digital wallet application, wherein the digital wallet application is implemented by the mobile device and the mobile device implements a payment application cooperating with the digital wallet application to perform a payment transaction with respect to the mobile payment card in the home banking network (H-NT), and the mobile device also implements a roaming payment application other than the payment application, the roaming payment application cooperating with the digital wallet application to allow adequate processing of a payment transaction with respect to the mobile payment card while roaming in the roaming payment network (R-NT); - receiving, by the second server (R-TSP) from the fourth server (R-SV), said roaming token (R-PAN) allocated to the mobile payment card for operating in the roaming banking network (R-NT); - obtaining, by the second server (R-TSP), based on the roaming token (R-PAN) and information previously stored in association with said roaming token (R-PAN), a home token (H-PAN) allocated to the mobile payment card for operating in the home banking network (H-NT) other than said roaming banking network (R-NT), said home token (H-PAN) being adapted to allow authentication in the home banking network (H-NT) of payment transactions performed by the digital wallet application; - receiving, by the first server (H-TSP), the home token (H-PAN) obtained by said second server (R-TSP); - obtaining, by the first server (H-TSP), based on the home token (H-PAN) and information previously stored in association with said home token (H-PAN), a primary card number (C-PAN) of the mobile payment card for operating in the home banking network (H-NT); and - sending, by the third server (H-SV), to a second bank system of an issuer of the mobile payment card, a transaction request comprising the primary card number (C-PAN) obtained by the first server (H-TSP) for allowing the payment transaction in the home banking network (H-NT) using said mobile payment card,