It means you (or someone else) have already submitted the same transaction ID to eRecruitment System. if it's your Transaction ID (assuming you are not trying to submit other's transaction ID!), please wait until your transaction is validated by employer organization.
At first check carefully whether application fee payment is mandatory for the post you are applying. if your post does not require paying application fee, then you cannot pay for that post!
If you need to pay for that post and you still can’t submit your payment transaction ID, then your transaction ID may be wrong. In that case take a snap of your transaction sms them mail to firstname.lastname@example.org .
Payment validation process may take 24 hours. It will require human attention to validate transactions with mobile banking system. After several hours, login to your account and check the payment summary, if the option is marked green and “yes” written then your payment is done..
You will get admit card only if you are shortlisted by the employer organization. You will get admit card via email, check the inbox of your email address (that is registered to eRecruitment portal). Alternately, you can download the admit card from your e-recruitment portal dashboard.