Photon working both online and offline

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9

I'd use something like this

const char jsonTemplate[] =           // string template for creating the JSON string
"{\"Timestamp_Device\":\"%d\""
",\"device_id\":\"%s \""
",\"temp\":\"%.1f\""
",\"flowshort\":\"%.1f\""
",\"flowacum\":\"%.1f\""
",\"vbat\":\"%.1f\""
",\"counterstatus\":\"%d\"}";

struct flowData_t {
  int      ts;                        // timestamp
  float    temp; 
  float    total;
  float    accum;
  float    vbat;
  int      status;
};
const int  maxBuf = 0x7F;             // (127) (power of 2)-1 for easy roll-over 
flowData_t flowBuf[maxBuf+1];         // allow for 0 .. maxBuf elements
int        head, tail;                // to use flowBuf as circular buffer

...
  char msg[sizeof(jsonTemplate)+64];  // allow for up to 64 characters to be inserted into the template
  while(tail != head) {
    snprintf(msg, sizeof(msg), jsonTemplate
            , flowBuf[tail].ts
            , (const char*)id
            , flowBuf[tail].temp
            , flowBuf[tail].total
            , flowBuf[tail].accum 
            , flowBuf[tail].vbat
            , flowBuf[tail].status);
    Serial.println(msg);
    tail++;                            // advance tail as we already treated that element
    tail &= maxBuf;                    // if tail reached end of array roll over when 
  }

This way you only store 24 bytes per set of data and create the actual string on the fly as automatic/local variable which will disappear as soon the function leaves.

When adding a new element to flowBuf[] you should do this

  head++;                     // advance head to next "free" position
  head &= maxBuf;             // when reaching the end of array roll over
  if (head == tail) {         // if the buffer is completely full overwrite oldest data 
    tail++;                   // advance tail one on as the previous entry will be overwritten
    tail &= maxBuf;           // roll over when needed
  }
  // fill data into flowBuf[head]

BTW, since it's not considered good style to put multiple instructions in one line you could rewrite this

as

      Serial.printlnf("backup: %d saved: %s ", o, (const char*)backup[o]);

Also there are neater ways to format this

e.g. like this

              if(config == 1)
                backup[o] = payload;
... 
              if(o == ARRAYSIZE-3) {         // if getting close to the limit delete everything . Id prefer to replace only the first..
                cleanbackup();               // resets all to "x"
                backupcounter = 0;
              }
              else 
                o = ARRAYSIZE+1;

Having conditional block of the same level also aligned on the same indent level makes code readability somewhat easier IMO.
Also adding some extra spaces adds readability - in exchange for the lost space the indentation depth could be reduced from 4 to 2 places.

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