Simply download and copy the plugin into the root directory of your server,enter credentials in your admin panel & you are done.

Step1: Download Paytm Payment Gateway PHP Kit
First you have to download Paytm Payment Gateway PHP Kit from given link. You need to copy PaytmKit folder in document root of your server.

Step2: Update Paytm Gateways Configuration
Now open config_paytm.php file from the PaytmKit/lib folder and update the below constant values:
{i} PAYTM_MERCHANT_KEY – Can be downloaded from the Paytm portal. One time downloadable
{ii} PAYTM_MERCHANT_MID – MID (Merchant ID) can be collected from Paytm team
{iii} PAYTM_MERCHANT_WEBSITE – Website name can be collected from Paytm team


define('PAYTM_ENVIRONMENT', 'TEST'); // PROD
define('PAYTM_MERCHANT_KEY', 'xxxxxxxxxx'); // Merchant key received from Paytm
define('PAYTM_MERCHANT_MID', 'xxxxxxxx'); // MID (Merchant ID) received from Paytm
define('PAYTM_MERCHANT_WEBSITE', 'xxxxxxxxxx'); // Website name received from Paytm


 
3.PaytmKit folder is having following files:
{i} TxnTest.php – Testing transaction through Paytm gateway.
{ii} pgRedirect.php – This file has the logic of checksum generation and passing all required parameters to Paytm PG.
{iii} pgResponse.php – This file has the logic for processing PG response after the transaction processing.
{iv} TxnStatus.php – Get the transaction status from API