Fatal error Mollie Woocommerce Fatal error: Uncaught Error: Call to undefined fu

Hi there,

I got an issue: After installation of the Mollie plugin, I could go to the settings page and insert the API Live. But as soon as I saved the configs, the following error occured and does not allow me to get to the settings of woocommerce or mollie anymore.
ideas on how to fix this?

Thanks!

Error when going to Mollie settings:
Fatal error: Uncaught Error: Call to undefined function json_last_error() in /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php:346 Stack trace: #0 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php(206): Mollie_API_Resource_Base->performApiCall(‘GET’, ‘methods?offset=…’) #1 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php(317): Mollie_API_Resource_Base->rest_list(‘methods’, 0, 0, Array) #2 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie/wc/helper/data.php(354): Mollie_API_Resource_Base->all(0, 0, Array) #3 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie/wc/helper/data.php(313): Mollie_WC_Helper_Data->getApiPaymentMethods(false, true) #4 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie/wc/helper/data.php(28 in /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php on line 346

Error when going to Woocommerce Logs:
2018-04-06T18:25:44+00:00 CRITICAL Uncaught Error: Call to undefined function json_last_error() in /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php:346
Stack trace:
#0 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php(206): Mollie_API_Resource_Base->performApiCall(‘GET’, ‘methods?offset=…’)
#1 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie-api-php/src/Mollie/API/Resource/Base.php(317): Mollie_API_Resource_Base->rest_list(‘methods’, 0, 0, Array)
#2 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie/wc/helper/data.php(354): Mollie_API_Resource_Base->all(0, 0, Array)
#3 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie/wc/helper/data.php(313): Mollie_WC_Helper_Data->getApiPaymentMethods(false, true)
#4 /var/www/sites/wp-content/plugins/mollie-payments-for-woocommerce/includes/mollie/wc/helper/data.php(28