Pixabay API integration is an Agency Feature. So, please make sure you have Promoyze Agency in your account. If you have Promoyze Agency in your account but still can't access Royalty Free Images, make sure you've entered the correct API key. In such case, remove the you have in the software settings, clear cache, delete cookies of your browser then, re-login your Pixabay Account, copy the API Key once again and enter in your Promoyze software settings. Close settings and restart the software.
If you don't have Agency in your account, please consider buying the Agency Upgrade in order to be able to use the Royalty Free Images feature.