CA sales tax and installment sales

[Summer2021]

Just noted that my client didn't accrue sales tax for fixed assets purchased through installment sales even though Form 8495 was filed.  The purchase will be paid in 5 equal installments and each installment is 6 months apart.  The 1st installment is scheduled to be due 9/30/23. Both buyer and seller agreed that buyer is responsible for sales tax.

For accounting purposes, I would assume sales tax is accrued on the date of purchase or the date asset was placed in service.

However, for sales tax payment purposes, when sales tax is due for an installment sale? Was it due when the sales contract was signed or when the payment is made?  

Any help or direction to an answer would be greatly appreciated.

[sjrcpa]

Didn't the seller  collect  it? 

EDIT: I missed "Both buyer and seller agreed that buyer is responsible for sales tax."