Have you read
https://docs.pact.io/getting_started/versioning_in_the_pact_broker
the provider version is set in your pact verification task, and provider versions are associated with verification results for a contract.
There are also two verification tasks.
one triggered by a consumer pact change, which may trigger multiple provider verifications against different versions (latest on main branch / any deployed or released provider). this would be one consumer version verified against many provider versions
one triggered by provider changes, which will dynamically fetch contracts from the broker (any consumer pacts on main branch and any deployed or released) - these would be many consumer versions verified against one provider version.