The first one is that you helped him. For example, you give him an early warning and help him figure out a solution to the problem. The quality of the project is no problem, and he passed the customs smoothly. Then this is a thank-you package, acceptable.
Second, you found a small problem that did not affect the quality of the paint. For example, the original requirement of paint thickness is 100, and his personal paint difficulty can only reach 80. He wants to send this question through a red envelope, so you should consider whether this question is the key. If not, just make a record, the red envelope should be collected.
Third, you found a big problem. This question violates the standard. It is best not to accept red envelopes. You can let him communicate with his superiors.
There are many problems in engineering. If you have rich experience, you will know which problems are important and which are small problems that do not affect the use.