Thanks Brian, but i have applied the Encode, but i have the same undesired result.
I think the issue is about the number of parameters or the length of the search instruction.
I'll keep waiting for someone to collaborate with the solution.

The interesting part is that there is no error, right? So whatever WebLink thinks the query is, it is a legal query. If it was too long or the date was invalid, you would expect an error to be reported. If you have Audit Trail you could see what the server thinks the search is.

if it is unfortunate that the weblink does not emit any type of error that could help us. if we have the Audit Trail, I will investigate and comment on the result.

I checked the Audit Trail and what is logged in it is different than the string I send, for example:
1. If I enter the modified date as the first parameter, the rest of the query string is omitted. it is only searched by the modification date.
2. If I enter the modified date after any parameter, the modified date and the rest of the statement are skipped. it only searches for parameters before the modification date.
Well, this is the end of the investigation, I believe that it is now in the hands of Laserfiche.

Gracias Brian.

If you open a support case, please reference this thread in your notes.