According to Sport, Real Betis want €30 million for Firpo, but Barcelona believe they can agree a deal closer to €20m.
Betis are reportedly keen for the deal to happen so that they can fund a move for Espanyol's Borja Iglesias.
The Seville-based side have also already signed a replacement for Firpo in Alfonso Pedraza from Villarreal.
Barcelona, meanwhile, are somewhat dependent on the sale of Rafinha to finalise a deal for Firpo.
Barça see the Dominican Republic-born player as an eventual successor to Jordi Alba on the left flank.
Firpo featured for Spain's European Championship-winning under-21s this summer and was previously eyed by Liverpool.
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