Not Working on WHMCS 8.0.2

[immdraselkhan]

Here is the error:

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Error: Undefined class constant 'MAJOR_VERSION' in /home/customer/www/omnisoftit.com/public_html/myaccount/vendor/guzzlehttp/guzzle/src/Utils.php:121 Stack trace: #0 /home/customer/www/omnisoftit.com/public_html/myaccount/vendor/guzzlehttp/guzzle/src/functions.php(61): GuzzleHttp\Utils::defaultUserAgent() #1 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/Coinbase/vendor/guzzlehttp/guzzle/src/Client.php(194): GuzzleHttp\default_user_agent() #2 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/Coinbase/vendor/guzzlehttp/guzzle/src/Client.php(75): GuzzleHttp\Client->configureDefaults(Array) #3 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/Coinbase/vendor/coinbase/coinbase-commerce/src/ApiClient.php(257): GuzzleHttp\Client->__construct() #4 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/Coinbase/vendor/coinbase/coinbase-commerce/src/ApiClient.php(236): CoinbaseCommerce\ApiClient->getHttpClient() #5 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/Coinbase/vendor/coinbase/coinbase-commerce/src/ApiClient.php(292): CoinbaseCommerce\ApiClient->makeRequest('POST', 'https://api.com...', Array) #6 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/Coinbase/vendor/coinbase/coinbase-commerce/src/Resources/Operations/CreateMethodTrait.php(21): CoinbaseCommerce\ApiClient->post('charges', Array, Array) #7 /home/customer/www/omnisoftit.com/public_html/myaccount/modules/gateways/coinbase.php(111): CoinbaseCommerce\Resources\Charge::create(Array) #8 /home/customer/www/omnisoftit.com/public_html/myaccount/vendor/whmcs/whmcs-foundation/lib/Module/AbstractModule.php(0): coinbase_link(Array) #9 /home/customer/www/omnisoftit.com/public_html/myaccount/vendor/whmcs/whmcs-foundation/lib/Module/Gateway.php(0): WHMCS\Module\AbstractModule->call('link', Array) #10 /home/customer/www/omnisoftit.com/public_html/myaccount/vendor/whmcs/whmcs-foundation/lib/Invoice.php(0): WHMCS\Module\Gateway->call('link', Array) #11 /home/customer/www/omnisoftit.com/public_html/myaccount/viewinvoice.php(0): WHMCS\Invoice->getPaymentLink() #12 {main}