Assalaamu alaykum. On your website, there is the following question: "I would like to know whether we can use forged certificates for any job?" Your answer included this citation: "Know that if having a genuine certificate is a condition to be accepted for the job, then it is not permissible to provide a forged certificate. If the people you want to work with consider the certificate a symbolic matter and experience is what is important for them, then you are allowed to work there."
In fatwa No. 234943, Islamweb said: "If the employer requires the certificate as a condition, that is, he would not have accepted the applicant for the job and would not have given him that salary, even if he has experience but does not have the required certificate, then it is not permissible for the applicant to work based on that certificate and he does not deserve that salary conditioned on the real certificate, even if he is experienced and competent."
My question is: Suppose that I have gotten a job using a genuine certificate. The employer requires the genuine certificate as a condition. However, I cheated during the exams to get that genuine certificate. Now I am doing the job properly, which proves that I am qualified to do the job. The employer is satisfied with my work. Is my income halal or haram?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It seems from your previous questions and what you mentioned in this question that you are suffering from Waswasah (obsessive/devilish whisperings). Waswasah is a disease which, if it overwhelms a person and he does not seek treatment from it, might ruin his life and religiosity, keeping him in constant distress and anxiety. The Islamic Shariah grants a legal concession for the person suffering from Waswasah to disregard the doubts that occur to him and refrain from acting upon them.

In brief, the answer to your question, regardless of the fatwas in reference, is that there is no harm in working in this job, and you are allowed to benefit from your salary as long as you carry out your work duties as required. As for the cheating that took place during the exams, it is sufficient that you ask Allah for forgiveness, regret what did, and resolve never to commit this sin again.

Shaykh Ibn Baaz was once asked:

"A student received a college degree, and he used to cheat in the different stages of education sometimes, either from notes or from his colleagues, which helped him receive his college degree. After graduation, he got a job based on his degree, and he receives a monthly salary; is this salary lawful or not? Note that he carries out his work duties very well and even works extra hours beyond the working hours. If his earnings are unlawful, then what should be done in this regard? What is your fatwa? May Allah reward you."

He replied, "This person has to repent to Allah from what he did and regret it. As regards his job, it is lawful, and his salary is lawful as long as he is carrying out the work duties that he is entrusted to do as required; praise be to Allah. But as we said, he must repent to Allah from the sin of cheating; verily, repentance wipes away the sins committed before it."

Allah knows best.