Smart Coupon not allowing product add to cart

Hi
I have WooCommerce Smart Coupons by Store Apps Version 3.8.1
Avada theme on Siteground hosting server.
Unfortunately no ADD to Cart shows up for one product in my woocommerce shop – its a a voucher for carmelc. It is supposed to have a field for the customer to fill in for any $ amount- and that should be allowed to Add to cart.

I dont know how long this has been an issue… but its not a problem for my other vouchers.

All coupons first loaded nearly a year ago, they are still connecting to the shopping cart fine.

Maybe this is an issue since updating woo to Version 3.5.1 yesterday (and all the other woo plugins), a note popped up: tested Smart coupons up to version 3.4.5.

I am mystified because it hasnt made all the other vouchers stop working.
As a precaution today I changed the sku name and coupon name to one word CarmelVoucher and removed hyphens and spaces from names.
I also tried to add Insert Smart Coupon code into the product but when saving page, it strips out the code as if it never were there.

Here is the full Woo Commerce warning notice:
PluginVersion 3.5.1 Tested up to WooCommerce version
PayPal for WooCommerce 3.4.5
Product CSV Import Export (BASIC) 3.4.5
WooCommerce – Store Exporter 3.4
WooCommerce Extra Product Sorting Options 3.4.4
WooCommerce Product Sort and Display LITE 3.4.0
WooCommerce Smart Coupons 3.4.5
WooCommerce Widget Product Slider LITE 3.4.0
Yoast SEO 3.4
WooCommerce – Product Importer unknown
WooCommerce Braintree Gateway unknown
WooCommerce Helper unknown
Woo Import Export unknown

Any suggestions would be gratefully received.
Regards

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