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We propose to perform two 170 ks INTEGRAL target of opportunity (ToO) observations of a transient millisecond X-ray pulsar in outburst. To constrain the broadband spectrum we also request one 30 ks simultaneous NuSTAR and two 50 ks XMM-Newton observations. The target can be either one of the twenty-one known transient accreting millisecond X-ray pulsars (AMXPs) under going a new outburst or a newly discovered object of this class. These observations will allow us to study the broad band spectrum from hard to soft X-ray energies as well as the timing properties or eclipsing features of the source during its outburst. The spectral information will make it possible to disentangle the contributions of soft black body reflection (if any) and hard Comptonized spectral components. Moreover we may detect type-I X-ray bursts and/or for the first time also burst oscillations at high-energy (if present). The INTEGRAL NuSTAR NICER Insight-HXMT Swift and XMM-Newton observations will also allow a timing analysis to study the pulse profile time lags and pulsed spectrum and will thus provide important constraints on emission mechanisms.Similar proposals were approved for the INTEGRAL AO2-AO18 cycles and during these years our ToO has been triggered ten times: in 2003 we observed XTE J1807-294 in 2004 2005 2009 2011 and 2013 we triggered on newly discovered sources IGR J00291+5934 HETE J1900.1-2455 IGR J17511-3057 IGR J17498-2921 and IGR J18245-2452 respectively. In 2015 we triggered on IGR J00291+5934 and SAX J1748.9-2021 and in 2018 we triggered again on a newly discovered source IGR J17591-2342 and Swift J1756.9-2508. [truncated! Please see actual data for full text]