Grid Legends - Upgrade problem

I’m looking for some help or advice. I have just started playing Grid Legends on PS5. I can’t figure out how to purchase the upgrade. I have done the required mileage in the Mustand GT4. When I go into the garage, I select that car and then tap the triangle to bring up the upgrade screen. Everything in the Stage 1 column is yellow/gold. The text at the top of each column, Stages 1, 2 & 3 is white (no longer transparent).  All of the items in the stage 2 & 3 columns are blue. When I click on any of them it says to  buy the previous upgrade to unlock.  But if I select any of the yellow stage one upgrades and press the x to buy, nothing happens. What am I doing wrong? I am getting to a point where the car is no longer competitive.

Thanks.