Error during umbrella sampling

GROMACS version:2020.1-Ubuntu-2020.1-1
GROMACS modification: Yes/No
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During umbrella sampling:
Distance between pull groups 1 and 2 (2.014074 nm) is larger than 0.49 times
the box size (1.568000).
How to resolve this error?

You need to make sure the length of the box in the direction you’re pulling is always larger than twice the distance between your pull groups. For example, if you know pulling groups 1 and 2 will reach a maximum of 4 nm apart, the box along that length must be at least 8 nm long