Complex sentence: Boniface tried to induce King Charles to break the treaty, but the latter was only too anxious for peace, and finally in May 1303 the pope ratified it (with changes and additions), Frederick agreeing to pay him a tribute.
Split into simpler sentences: Boniface tried to induce King Charles to break the treaty, but the latter was only too anxious for peace. Finally, in May 1303, the pope ratified the treaty, albeit with changes and additions, which included Frederick agreeing to pay him a tribute.