Inclusion Criteria:  Diagnosis of fibromyalgia syndrome (ACR criteria 2016). Chronic widespread musculoskeletal pain symptoms (>1 location using the Widespread Pain Index). High-intensity pain (VAS ≥ 4), at least 3 days a week for the previous 3 months. If currently taking analgesic or psychotropic medications, they had to be stabilised for four or more weeks before the study enrolment Over 18 and less than 65 years old (labour active). Ability to speak and understand English or Spanish.  Exclusion Criteria:  Acute or temporal pain Severe cognitive impairment, detected by the Mini-Mental State Examination (score <24 out of 30 points) Severe mental disorders in acute phase or symptomatic phase Behavioural alterations as this may interfere in their participation Severe intellectual disability Other severe or medically unstable diseases interfering with the project participation Co-occurrence of neuropathic pain Other disorders that may cause pain Pregnant or breast-feeding Drug abuse within the past year.