@spec get_payment_link(map()) :: String.t()

Takes a map of payment details and returns a KNET payment link. The payment_details map should contain the following required keys:

• knet_username
• knet_password
• knet_key
• amount
• response_url
• error_url
• track_id

The following keys are optional:

• knet_url (defaults to https://kpay.com.kw/kpg/PaymentHTTP.htm)
• currency_code (defaults to 414)
• lang. Could be ENG or AR (defaults to ENG)
• udf1 to udf5 (user defined fields). These are optional and will be returned back to you in the response.