Settings greyed out and activation of Polylang Pro

Hello,

I am managing a site developed by a third party and I want to buy a PolyLang Pro license. However, when I go to settings (on WordPress), the License keys option is grayed out.

All the translations of the site are already in place si how do I activate PolyLang Pro?

I precise that the developpers installed these extensions as well:

– Hyyan WooCommerce Polylang Integration
– Theme and plugin translation for Polylang (TTfP)
– WPML to Polylang

Is there a way to activate Polylang Pro (in order to benefit the same slug feature) without losing my translations and without causing any conflict with the other plugins?

Thank you.