In Account object, i have a picklist field " Account status" with values as active, blacklisted. bydefault, while creation its active, I want that if the value is changed to blacklisted, It shouldnt allow to create a new opportunity in teh related list, and give a message that " account is blacklisted". Also, on the existing opportunity, when one entered, it shouldnt allow to edit the opp, and give teh same above message. Can anyone plz suggest a good way to do this. I tried to use the process builder ( auto approval process), and approval process, while the value is changing , its locking the existing opp. But the drawback on my process is that,

1. Its keep allowing to create a new opp, and then unlocking it, which i dont want. from beginning it shouldnt allow and give the error message.
2. for the existing opp, its allowing to edit first time before unlocking it.
3. No error message i able to set anywhere. Thnx

In Account object, i have a picklist field " Account status" with values as active, blacklisted.

by default, while creation its active, I want that if the value is changed to blacklisted, It shouldn't allow to create a new opportunity in the related list, and give a message that " account is blacklisted". Also, on the existing opportunity, when one entered, it shouldnt allow to edit the opp, and give teh same above message.

Can anyone plz suggest a good way to do this. I tried to use the process builder ( auto approval process), and approval process, while the value is changing , its locking the existing opp. But the drawback on my process is that,

1. Its keep allowing to create a new opp, and then unlocking it, which i dont want. from beginning it shouldn't allow and give the error message.

2. for the existing opp, its allowing to edit first time before unlocking it.

3. No error message i able to set anywhere.