How do we resolve the following error message?
Uncaught Error: Call to a member function getCheckoutApi() on null in …
Do you have more of the error message or the body of the request so we can take a closer look? 
As requested, you may refer to the following error. I’ve tried solving this matter to no avail. for several hours.
We are not able to receive payments from our clients to-date because of the migration from SqPaymentForm to Web Payments SDK.
We are using the Web Payments SDK PHP project that Lance from the Square Web Development team provided. [PHP Payment Example Project] connect-api-examples/connect-examples/v2/php_payment at master · square/connect-api-examples · GitHub
ERROR MESSAGE:
Fatal error : Uncaught TypeError: Square\ApiHelper::appendUrlWithTemplateParameters(): Argument #1 ($url) must be of type string, null given, called in /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/vendor/square/square/src/SquareClient.php on line 304 and defined in /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/vendor/square/square/src/ApiHelper.php:47 Stack trace: #0 /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/vendor/square/square/src/SquareClient.php(304): Square\ApiHelper::appendUrlWithTemplateParameters() #1 /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/vendor/square/square/src/Apis/LocationsApi.php(176): Square\SquareClient->getBaseUri() #2 /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/utils/location-info.php(32): Square\Apis\LocationsApi->retrieveLocation() #3 /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/utils/location-info.php(51): LocationInfo->__construct() #4 /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/index.php(3): include(‘…’) #5 {main} thrown in /webroot/f/l/flocc001/acceptpayment.net/www/giftcards/payment/vendor/square/square/src/ApiHelper.php on line 47
It sounds like the SquareClient.php isn’t correctly configured. Were you first able to get it working by just following the README.md?
We relaunched COMPOSER UPDATE and executed the following command line script.
php composer.phar install
After executing the above command line script, a Vendor folder was created with various dependencies (or other folders and files)
Please help!
Great! Did you then create a new file .env by copying the contents of the .env.example file and edit this file with your application credentials and environment configuration. WARNING : never save your credentials in your code.
Yes, the .env file was updated accordingly or as directed.