I'm using paypal to be paid online.
I added the "make payment" link to the invoice but I noticed that when opening the paypal link to pay the invoice the amount doesn't automatically show up on the paypal payment page.

I'm left with a blank field where I have to enter myself the amount to pay.

I'm  confident this is just my mistake,
what am I doing wrong?

I would like to have simple link leading to a paypal page with the amount already set to the invoice amount.

thanks
Bruno