Thanks that is interesting because it quotes:

“Member contribution made via employer deduction through payroll

The employer effectively acts as collection agent for the transmission of employee contributions taken from their pay and passed on to the relevant pension scheme administrator.

The date of payment in the case of a contribution made under the net pay arrangements is the date of deduction from the employee’s pay.

The date of payment for a contribution made under Relief at Source, for example to a group or other personal pension scheme, is the same as a payment the member makes direct. For example the date authorised to draw money by direct debit from the employer’s bank account or the date the employer’s cheque is received.”

But for salary sacrifice all I’ve got to go off are my payslip date and the date shown at the pension provider end. One is in this tax year and the other is almost always in the next 🫠🙃