Is it possible to pay the conference fee at the end of the year even if the conference itself will not take place until the following year?

These costs can only be recognised if they are accrued. In the context of the current year's spending (at the end), they cannot be recognised, as the earmarked support of the year cannot be used to cover the next year's expenditure.

An exception to this would be where the conference fee was paid directly by the participant at the end of the year and would only be charged to the project costs as part of the travel voucher and travel settlement. In this case, it would be appropriate to attach (in addition to the other documents) a bank statement and an affidavit from the participant that the items have been paid.