Hello @Aveeva
This is a pre found issue in Magento :
https://github.com/magento/magento2/issues/12612
you can try with below solution if it works for you :
https://magento.stackexchange.com/questions/213517/array-to-string-conversion-in-magento-2
if it doesn't work then take pull from fixed branch of Github or get the changes which they did, it will resolve your problem.
