Submit price to PayPal

Hello and thank you for this plugin.
It works fine, but I’m not able to submit a price to PayPal.
In my form there is a “radio selection” with different prices.

In “Item Price” I con put in e.g. 10.00 and it works.
When I put in “[radio-price]” an error occures.

What is the right way, to submit the correct price to PayPal?

Thank you very much for a short message.

Steve

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