Hi,
The tax point of a service is usually determined by when the service is performed. This is the basic tax point. However, if a payment is received before the basic tax point then this payment will create a tax point. This is the actual tax point.
The tax point can be also effected by the raising of a VAT invoice but this will only be relevant where the business raising the invoice is VAT registered.
Therefore in your case the tax points will be created by the payments made to you. You can see the guidance here:
Time of supply (tax point) rules
Thank you.