500 Internal Server error when OPTIMA is trying to access product page

Hi,
we are trying to sync our ecommerce to our 3rd party fulfilment warehouse through a software called Optima.

I have created the API key as Admin and followed all instructions given by Optima but whilst they don’t see an error when they access https://pistachiobee.com/wp-json/wc/v2/orders, they get ‘500 Internal Server error’ when OPTIMA is trying to access https://pistachiobee.com/wp-json/wc/v2/products.

I have reset permalinks but it is not working.

Can you help please?

Thank you

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