pixel_player422146491 I'm sorry for my late reply. I also had this problem, and I learned something when I was investigating the issue.
I've been a victim of identity theft, and I absolutely refuse to associate a credit card with my android device. (or any other piece of personal electronics)
I also use a Google card to make purchases through the Google Play Store. This does include making purchases through apps like Seaport.
The answer to your dilemma is tax.
This is not something that pixel federation has control of.
An example of this is...
...You're wanting to make a 9.99 purchase with Seaport.
...you have 10.00 applied to your Play Store account.
You'd think that the purchase would go through, but you are dismayed that it has been declined. And it doesn't indicate the reason why. What has happened is tax has been applied to the purchase but it doesn't tell you so. If you have enough to cover this tax the purchase will go through but it doesn't indicate that you spent it. You can determine how much tax has been applied to your purchase by comparing the amount on your account both Before & After purchase.
If you had 11.00 on your account, the 9.99 purchase would have gone through.
. . . voice of experience . . .