PayPal yearly recurring option not working

Hello, I have many times succesfully implemented several forms of payment options via Paypal with your plugin, but I have a problem with a yearly membership. I have selected Recurring ′Yearly′ at the contact form Paypal settings, but when I test the annual membership option, PayPal says that I will be charged monthly instead of yearly.

I hope you can help me asap.
Thank you.
Nicole

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