Please check the following:
- "Error Log - Payments2us". There might be an error in here that describes an issues. This is likely to be a restricted Picklist, Validation Rule, Flow/Process Builder issue (NOTE: Issues caused by these are outside the scope of Payments2Us Standard support)
- The Batch Processor might need to be stopped/started.
- Receipting might be set to Manual or Similar. See Checkout FAQ for Payment Txns being stuck.
- The user that started the Batch Process might not have a Payments2Us Permission Set assigned.
- Perhaps the Opportunity was created and then later deleted. Please check your Recycle Bin for the Opportunity.