Fans have complained of sound issues for the second time on the Spice Girls' reunion tour.
The pop group's performance on Monday evening at the Principality Stadium did not go down well with some attendees, who claimed they could not hear the music properly.
It comes after similar problems were reported during their opening concert at Dublin's Croke Park on Friday night.
After disgruntled fans who paid £96 for tickets vented their anger online, Mel B acknowledged the issues and said she hoped "the vocals and the sound will be much, much better".
But attendees in Cardiff disagreed, with one writing: "Okay so @spicegirls was so much fun however the sound was atrocious and you could not hear what they actually said! So disappointing when you pay soo much for a once in a life time opportunity."
Another wrote: "@spicegirls how disappointing to spend money on a ticket to see you @principalitysta and the support act stole the show! Sound was pants!"
Others claimed they "couldn't hear half of it", with some demanding a refund.
Reaction to the Cardiff gig has been mixed online, with some fans tweeting to say that they had enjoyed a "phenomenal" evening and had not noticed any sound problems whatsoever.
Brown, Emma Bunton, Geri Horner and Melanie Chisholm - also known as Scary, Baby, Ginger and Sporty Spice - are performing 13 dates on the Spice World tour.
It is the first time the girls have reunited since their performance at the closing ceremony for the 2012 London Olympics.
After Cardiff, they are next set to perform at Manchester's Etihad Stadium, the Ricoh Arena in Coventry, Sunderland's Stadium of Light, the BT Murrayfield Stadium in Edinburgh, Bristol's Ashton Gate Stadium and Wembley Stadium in London.
© Sky News 2019